This invention relates generally to electrical circuits, and more particularly to apparatus and methods for providing an increasing power supply voltage.
Several different types of electronic devices can utilize an increasing voltage supply. One such example is a one-time programmable electric fuse, which is a type of non-volatile memory. An electric fuse can be used to provide memory for chip ID, configuration settings, feature selection, etc.
One type of voltage supply switch for providing an increasing voltage supply is based on a digital approach. FIG. 1 is a diagrammatic representation of a digital voltage supply switch 150. In general, a circuit that implements this approach includes an oscillator (CLK), counter 122, decoder 124, and resistive network 112 for normal operation.
According to a required ramp-up slew rate, a time period is determined by a counter 122 and a decoder 124. In every such period, the proper switch 112, e.g., selected from switches RN0-RNn, is closed and an appropriate gate voltage, e.g., VG0-VGn, is imposed on a corresponding power transistor. Module 106 contains a system of power transistors P0-Pn. In summary, each of the power transistors corresponds to a different switch (RN0-RNn) path. An output voltage VDD_OUT is then supplied to load 104.
The output voltage VDD_OUT profile for this circuit has a staircase shape as illustrated in the graph 200 of FIG. 2. The lowest voltage stair is obtained when all the power transistors are switched off. Every pulse that is provided by the decoder (124) turns on a successive power transistor, which each yield a new voltage stair, e.g., BUF0-BUFn. Eventually, the voltage output staircase wave, VDD_OUT, reaches its target peak voltage, VDD_IN-IR drop. Although this digital approach achieves a particular voltage output slew rate, such implementation is very sensitive to the process parameters, temperature, output load 104 and resistive network 112, as well as requiring a clock (CLK).
Improved voltage switch devices for providing an increasing output voltage rise with a programmable slew rate would be beneficial.